(1) Field of the Invention
This invention relates to an apparatus for classifying particulate material under a controlled atmosphere. The apparatus of the subject invention is particularly suited for classifying powdered metal by size and removing particles of undesirable material of lower density than the metal particles.
In the processing of certain powder metals, such as nickel, titanium and cobalt-base superalloys, it is necessary to separate the powdered metal particles into size ranges. For example, the particles may be cold-worked by the introduction of strain energy into the individual particles of the powder metal by deforming the particles between a pair of rolls in a rolling mill. So that all of the particles which pass between the rolls of such a roll mill are deformed, they must be of a relatively similar size or in a size range.
(2) Description of the Prior Art
There are assemblies known in the prior art for classifying particulate material by use of a stream of gas impinging upon the particles whereby the smaller or less dense particles will have greater trajectories than the larger or more dense particles. However, such assemblies do not provide the desired preciseness in classification of the various particle size ranges because the gas stream and the gas stream path result in turbulence and eddy currents which interfere with the desired classification. Further, the prior art assemblies are to a degree deficient in the separation of the various particles because the particles may group or cluster together which, of course, reduces the preciseness in the classification.